Embodiments of the present invention relate to non-volatile memory devices and their methods of manufacture.
Non-volatile memory devices, such as flash memories, are capable of retaining or storing charge without external power. A flash memory comprises an array of memory cells, each of which is configured to store a bit of information corresponding to a charge or gate threshold voltage. Newer flash memory devices can even store several bits of information per cell using parameters that exhibit more than two distinct levels.
Flash memory devices are of different types depending on their structure for storing charge. One type, commonly known as a floating gate memory, stores charge in a floating gate electrode disposed under a control gate electrode. However, in these devices, the conductive floating gate electrodes are electrically isolated for data retention, and the resultant gate structures have high aspect ratios that are hard to fabricate. Also, at higher aerial or device densities, the spacing between adjacent floating gate cells becomes very small. The smaller spacing can result in electrical coupling between adjacent cells and cause dissipation of the charge retained in these cells.
Another type, commonly known as the charge trap type flash memory, uses a gate insulating layer formed of silicon nitride to provide charge trap sites. Charge trap memories are advantageous as they can be manufactured with fewer process steps. However, as these devices become smaller, the net area of the trapping site or individual charge trap cell is reduced. The smaller area of the charge trap cell allows a smaller number of electrons to be loaded onto the charge trap cell. The decrease in electron holding capacity of each charge trap cell decreases the amount of information that may be stored in the cell.
For reasons that include these and other deficiencies, and despite the development of various flash memory devices, further improvements in memory devices and charge trap cells are continuously being sought.